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IntermediatePublished 2026-06-25

Extending VLAN 10 Across Two Switches (802.1Q)

Bundle lab

Build and verify an 802.1Q trunk between two access switches that cleanly transports VLAN 10 end-to-end while intentionally pruning VLAN 20. You will configure access ports, create VLANs, set a hardened dot1Q trunk with a non-default native VLAN, and validate host reachability and isolation from endpoints.

Track
Est. time
55 minutes
Difficulty
Intermediate
Topics

Learning objectives

  • Create VLANs and assign switch access ports to the correct VLAN
  • Configure and harden an 802.1Q trunk with an explicit allowed VLAN list and a non-default native VLAN
  • Verify correct VLAN transport over the trunk and isolation for pruned VLANs
  • Validate host-to-host connectivity within VLAN 10 across two switches from real endpoints
  • Troubleshoot native VLAN mismatches, allowed-VLAN pruning errors, and host-to-port/VLAN misassignments

Troubleshooting focus

  • CLIENT10-A cannot ping 10.10.10.20 across the switches: confirm each host-facing port is in access VLAN 10, not VLAN 1. show vlan brief and show interfaces switchport are your friends.
  • The ping still fails with both access ports correct: compare show interfaces trunk on both sides. If one switch prunes VLAN 10 from its allowed list, inter-switch forwarding for that VLAN breaks.
  • Console warnings about a native VLAN mismatch, plus odd untagged behaviour: one end is on 99 and the other on 1.
  • Ethernet0/3 never comes up as a trunk: DTP negotiation is enabled on one side and disabled on the other.
  • The configuration reads correct but the wrong ports are affected: verify the physical ports in use. E0/3 is the trunk on both switches, E0/0 is the VLAN 10 host port on both, and E0/1 on SW-SITEA-ACC1 only is VLAN 20.

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Learn VLANs, Trunking & Inter-VLAN RoutingWhat Is a VLAN? VLANs Explained for Beginners

Grade your work

How this lab is graded
  • Build it your way. Where a lab lets you choose a value — a VLAN name, an interface description — grading checks that you configured it, not which name you picked. Names that another line has to reference, like an ACL applied with access-class, are stated in the guide and do have to match.
  • Addresses, modes and protocol keywords are exact. An IP address, a subnet mask, switchport mode trunk, an encapsulation — these carry the meaning of the lab, so they are graded as written in the guide.
  • Grading reads your saved configuration. Export the lab from CML after you have configured it, and make sure anything you set is in the running-config — a change that only exists in a terminal session never reaches the grader.
  • You can submit as many times as you like. Your best score stands, and each attempt tells you which checks passed so you can work the gaps.
  • Scored something you believe is correct? Use Report an issue on this page — that is exactly how the grading fixes in the changelog got found.

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